When hamsters are healed neonatally with the synthetic estrogen, dethylstibestrol (UES), their uteri consistent exhibit a severe hyperplastic/neoplastic response to estrogen in adulthood. One of two alternatives working hypotheses should explain this phenomenon: 1) Direct Action The cellular physiology and/or composition of the neonatal hamster uterus is directly and permanently altered by the DES insult such that the adult organism overall proliferative response to estrogen becomes atypical, or 2) Indirect Action Uterotrophic activity is mediated by estrogen primarily through or in conjunction with other unidentified factors, and neonatal DES treatment permanently alters the level or functional activity of such factors. Testing these hypotheses will begin (Specific Aim #1) by monitoring the morphogenesis of neonatal uteri from control and DES healed donot animals that are transplanted into the contralateral cheek pouches of control and DES-treated mature hosts that are ovariectomized and estrogen- replaced. To confirm and extend the findings (Specific Aim #2), homotypic and heterotypic recombination of uterine stroma and epithelium from control and DES-treated animals will be performed and their morphogenesis will be studied: a) in vitro using media supplemented with uterine tissue extracts and/or serum from the same host groups used in Specific Aim #1 and b) in vivo (within the cheek pouch) using the same host groups as in Specific Aim #1. Because this combination of approaches relies on few, if any, a prior assumptions and accommodates both in vivo and in vitro observations, firm conclusions should be reached about which alternative hypothesis is most valid. Lastly (Specific Aim #3), we will test whether altered expression of known regulatory genes is involved in the atypical estrogen responsiveness of adult uteri in neonatally DES treated hamsters. We will begin with the c-myc c-tos and c-jun proto-oncogenes plus the p53 anti- oncogene. Their expression will be probed at the RVA and protein level as well as at the whole-organ and cell specific level using Northern blot analysis, in situ hybridization, immunoprecipitation/Western blot analysis and immunohistochemistry. Together these studies should contribute significantly to our long-term objectives of 1) understanding the basic mechanisms whereby estrogen regulates uterine growth and morphogenesis and 2) identifying mechanistic alterations that are responsible for degeneration of this process to the unregulated neoplastic state. These are biomedically important because 1) successful conception and gestation demands normal uterine form and function, and 2) estrogen-dependent uterine neoplasms ar responsible for considerable morbidity and mortality in contemporary American society.